fix(content-blog): generate feed by reading build output (#6454)

packages/docusaurus-utils/src/index.ts

@@ -23,7 +23,6 @@ import {simpleHash, docuHash} from './hashUtils';
 import {DEFAULT_PLUGIN_ID} from './constants';
 
 export * from './constants';
-export * from './mdxUtils';
 export * from './urlUtils';
 export * from './tags';
 export * from './markdownParser';
@@ -210,6 +209,39 @@ export function getPluginI18nPath({
   );
 }
 
+/**
+ * @param permalink The URL that the HTML file corresponds to, without base URL
+ * @param outDir Full path to the output directory
+ * @param trailingSlash The site config option. If provided, only one path will be read.
+ * @returns This returns a buffer, which you have to decode string yourself if
+ * needed. (Not always necessary since the output isn't for human consumption
+ * anyways, and most HTML manipulation libs accept buffers)
+ */
+export async function readOutputHTMLFile(
+  permalink: string,
+  outDir: string,
+  trailingSlash: boolean | undefined,
+): Promise<Buffer> {
+  const withTrailingSlashPath = path.join(outDir, permalink, 'index.html');
+  const withoutTrailingSlashPath = path.join(outDir, `${permalink}.html`);
+  if (trailingSlash) {
+    return fs.readFile(withTrailingSlashPath);
+  } else if (trailingSlash === false) {
+    return fs.readFile(withoutTrailingSlashPath);
+  } else {
+    const HTMLPath = await findAsyncSequential(
+      [withTrailingSlashPath, withoutTrailingSlashPath],
+      fs.pathExists,
+    );
+    if (!HTMLPath) {
+      throw new Error(
+        `Expected output HTML file to be found at ${withTrailingSlashPath}`,
+      );
+    }
+    return fs.readFile(HTMLPath);
+  }
+}
+
 export async function mapAsyncSequential<T, R>(
   array: T[],
   action: (t: T) => Promise<R>,